GFS vs ECMWF Demand-Hub Outlook: 2026-04-06T00:00Z

Executive Summary

The 15-day outlook has trended significantly warmer (less demand-intensive) compared to the prior cycle, with both models shedding substantial heating demand. The GFS and ECMWF present conflicting solutions, with the GFS showing a colder Midwest and hotter South, while the ECMWF is warmer in the Midwest and East. This divergence results in low forecast confidence, particularly for the back half of the period.

Hub-Level Weather

The primary drivers of the national forecast show significant model disagreement:

• Midwest (Chicago, 35% weight): The ECMWF is notably colder than the GFS, projecting 197.9 cumulative HDDs versus 180.4 from the GFS. The largest daily differences occur late in the period (e.g., April 18-20).
• East (New York City, 30% weight): The models are inverted here, with the GFS forecasting a colder outlook at 174.0 cumulative HDDs, while the ECMWF is much warmer at 151.8 HDDs. The ECMWF also projects significantly more late-period warmth, with 21.7 cumulative CDDs versus just 2.9 from the GFS.
• South Central (Houston, 15% weight): This is the key driver for cooling demand. The GFS is substantially hotter, forecasting 157.5 cumulative CDDs compared to the ECMWF's 102.4 CDDs.

Demand Implications (Natural Gas)

The forecast suggests a classic shoulder season profile, with front-loaded heating demand giving way to back-ended cooling demand.

• Heating Demand: Both models show a significant drop in heating demand versus the prior run (GFS -30.3 weighted HDDs; ECMWF -70.0 weighted HDDs). While the GFS projects a slightly higher national total (146.9 weighted HDDs vs. ECMWF's 140.4), the overall signal is for below-normal heating load for this time of year.
• Cooling Demand: Cooling demand builds in the South and Southeast, but the magnitude is uncertain. GFS is more aggressive, projecting 39.0 weighted CDDs nationally, largely driven by its hot solution in Texas. The ECMWF is more muted at 35.4 weighted CDDs.

Model Agreement & Caveats

Forecast confidence is low due to significant model disagreement and recent run-to-run volatility.

• Convergence: The model agreement is poor, reflected by a low convergence score of 0.21. A weighted mean absolute HDD difference of 3.7 per day highlights the material differences between the forecasts.
• Run-over-Run Shift: The forecast underwent a major revision warmer. The ECMWF shed 70.0 weighted HDDs and the GFS lost 30.3 weighted HDDs from the prior cycle. This level of volatility suggests the atmospheric pattern is not well-resolved and further significant changes are possible.
• Source Note: This analysis is based on deterministic runs from the GFS and ECMWF models via Open-Meteo. Ensemble guidance should be consulted for a more complete probabilistic view of potential outcomes.